Liquid crystal displays (LCDs) are used in portable personal computers (PCs) and other electronic devices to display information. LCDs modulate light to create images using selectively transmissive and opaque portions of the display, the selection being controlled by passing electrical current through the liquid crystal material. Transmissive-type LCDs are illuminated by an artificial backlight positioned behind the LCD glass to provide the contrast between the light transmissive and opaque portions of the display.
The LCD backlight is one of the primary sources of power consumption in a portable PC and the power consumed by the backlight is directly related to the brightness level selected. Therefore, it would be advantageous, from a power consumption standpoint, to operate the PC with the LCD at the lowest possible brightness level at which the contents of the display can still be seen by the user. For example, in a particular portable PC model available from Dell Computer Corporation of Austin, Tex., operating the PC with the LCD set to the minimum brightness level, as compared to the maximum brightness level, can reduce overall power consumption of the PC by approximately twenty percent (20%), which in turn increases the runtime of the PC between battery charges by the same percentage. Specifically, assuming that in the example just described the PC has a typical runtime between battery charges of 8 hours with the LCD set to the maximum brightness level, decreasing the brightness level to the minimum level will increase the runtime of the PC to 9.6 hours.
In view of the foregoing, it is apparent that a user could significantly increase the runtime between battery charges of his or her portable PC by taking advantage of ambient lighting conditions that increase the visibility of the LCD, that is, low ambient light, and decreasing the brightness level of the LCD whenever the PC is being operated in such lighting conditions. Specifically, it is obvious that the contents of an LCD can be much more easily viewed in a dark room than a bright one. Hence, a user could take advantage of that fact by decreasing the brightness level of the LCD whenever ambient lighting conditions permit and then subsequently increasing the brightness level only when necessitated by bright ambient lighting conditions.
While foregoing manual brightness adjustment presents a viable option for increasing the runtime of a PC between charges, it is deficient in certain respects. In particular, while a user may begin by operating the PC with the LCD brightness set to the minimum level necessary to enable the contents of the display to be perceived, after a user has moved with the PC to an environment in which the ambient lighting conditions require that the LCD be set to the maximum brightness level, the user will typically forget to decrease the brightness level upon returning to an environment in which the ambient lighting conditions would be conducive to such a decrease. As a result, the power savings are not as substantial as might be the case were the brightness adjustment to occur automatically.
Accordingly, what is needed is an intelligent LCD brightness control system which automatically adjusts to the ambient lighting conditions of the environment in which the PC is being used.